Field of Invention
The present invention relates to a display device with a wide viewing angle. More particularly, the present invention relates to a wide viewing angle display device utilizing light diffraction to improve a viewing angle of a display device.
Description of Related Art
With the advance of the fabrication technology of thin film transistors, liquid crystal display (LCD) devices are generally applied into variable electronic products such as televisions, personal digital assistants, notebooks, digital cameras, video cameras and recorders, and mobile phones, etc, because the LCD devices has advantages of brightness, thinness, low power consumption, and no harmful radiations, etc. However, since the LCD device is not a self-luminous display, a backlight source is required to generate light for the LCD device, and the light is guided to pass through optical films such as diffusion layers and brightness enhancement films (BEF), thereby forming a uniform planar light emitted into a liquid crystal display panel to enable the LCD device to show images. Twisted nematic (TN) or super twisted nematic LCD devices are popular displays of common displays. The TN and STN liquid crystal display devices have an advantage of competitive price, but a visual angle thereof is smaller than that of wide visual angle LCDs (for example, multiple-domain vertical alignment (MVA) displays, in-plane switching (IPS) displays, and fringe field switching (FFS) displays, etc).
The visual angle means an angle range in which the display can show images with good quality. For example, with respect to a desktop display, users often look at the desktop display in a normal viewing angle. Because different alignments of liquid crystal molecules lead to different optical effects, when designing the displays, designers take the image quality of the display corresponding to the normal viewing angle as a main consideration. Therefore, when looking at the display in an oblique viewing angle, an observer can find the difference between images observed in the normal viewing angle and the images observed in the oblique viewing angle (such as brightness difference or chroma difference), and the difference becomes greater with increase of a viewing angle of the observer. In common liquid displays, TN liquid displays have the worst situation about the visual angle problem mentioned above.
Referring to FIG. 1, FIG. 1 is a diagram showing the structure of a liquid crystal layer 12 of a TN LCD 10. The TN LCD includes the liquid crystal layer 12, an upper alignment plate 14, and a lower alignment plate 16, wherein the lower alignment plate 16 is disposed closer to a backlight source than the upper alignment layer 14. The liquid crystal layer 12 includes top layer liquid crystal molecules 12a and bottom layer liquid crystal molecules 12b. The upper alignment plate 14, and the lower alignment plate 16 are used to align the top layer liquid crystal molecules 12a and the bottom layer liquid crystal molecules 12b. Therefore, a twisted structure having a pre-tilt angle is formed, wherein a terminal of a liquid crystal molecule having the pre-tilt angle is referred to as a “head terminal”, and the other terminal thereof is referred to as an “end terminal”. For example, the upper alignment layer 14 aligns the top layer liquid crystal molecules 12a, so that the top layer liquid crystal molecules 12a have the pre-tilt angle. For another example, the lower alignment layer 16 aligns the bottom layer liquid crystal molecules 12b, so that the bottom layer liquid crystal molecules 12b have the pre-tilt angle. The alignment directions of the alignment layers 14, 16 are not parallel to each other, so that the liquid crystal molecules locate there between are continuously twist-aligned in a direction from the alignment layer 14 toward the alignment layer 16. Accordingly, the twisted angle of the liquid crystal molecules can be defined as an angle between the head terminals of the bottom layer liquid crystal molecules and the end terminals of the top layer liquid crystal molecules.
In addition, the terminals of the liquid crystal molecules forming the twisted liquid crystal structure (including the head terminal of the bottom layer liquid crystal molecules 12b, the top layer liquid crystal molecules 12a, and the liquid crystal molecules located there between) define a viewing area. For common TN LCDs, a viewing angle range corresponds to such viewing area has bad optic characteristics. The viewing angle range is usually defined as a downward viewing angle for the observer. Of course, the viewing angle range with bad optic characteristics can also be defined as another viewing angle for the viewer (except for the normal viewing angle) depending on application demands.
For a TN LCD in which no viewing angle compensation mechanism is applied, images observed in an oblique viewing angle of the TN LCD have the problems regarding contrast (smaller than 10), gray level inversion, and color shift. In order to solve the problems of the TN LCD, compensation films are added in the TN LCD, thereby improving the quality of the images observed in the oblique viewing angle. The compensation films may be, for example common Fuji wide view films (WV films) developed by Fujifilms. The Fuji wide view films are common compensation films used in the TN LCD. However, great improvement about the contrast and less color shift can be achieved by the WV films, but only little improvement about gray level inversion is achieved by present compensation film. Therefore, the TN LCD is not considered as a wide visual angle LCD.
Therefore, there is a need to provide a display device which can improve the image quality problems about brightness and chroma, including contrast, deviation of gamma curve, and color shift issues, etc., and more particularly, when a TN LCD is applied in a display device, the novel display device can be used as a wide visual angle LCD and has advantages of lower cost, and higher response speed comparing to the LCDs in the LCD market.